The present invention generally relates to a method of hardening a work piece, and more particularly relates to a method of hardening a bushing of a track chain.
Some work machines, such as a bulldozer, typically have a sprocket, an idler, a track chain, and a number of track shoes attached to the track chain for propelling the work machine over the ground. Track chains generally include a pair of parallel chains, with each parallel chain being made up of a series of entrained track links. Track chains further include a number of pin and bushing assemblies in which a pin is positioned within a passageway defined in a bushing. Each pin and bushing assembly is interposed and connected to the parallel chains.
During use of the work machine the sprocket rotates and engages the bushings of the track chain, thereby causing the track chain to rotate around a path defined by the sprocket and the idler. The rotation of the track chain causes the track shoes to engage the ground, thereby propelling the work machine over the ground to perform various work functions.
A problem with the above described arrangement is that the bushings are subjected to many cyclic loads as the track chain is rotated around the sprocket and the idler. For example, as the track chain rotates around sprocket and the idler, the inner diameter of each bushing is subjected to cyclic loads from the pin as the bushing rotates relative to the pin. In addition, the outer diameter of each bushing encounters cyclic loads as each bushing engages the sprocket. The cyclic loads cause the bushings to wear which increases the cost of maintaining the work machine.
One way of reducing the wear of the bushings is to subject them to a hardening process. For example, U.S. Pat. No. 5,702,667 discloses an apparatus for simultaneously heat treating the outer peripheral surface and the inner circumferential surface of a bushing. However, the process described in the U.S. Pat. No. 5,702,667 does suffer from the drawback that it is difficult to control the characteristics of the resulting hardened areas when the outer peripheral surface and the inner circumferential surface are simultaneously heat treated. In addition, the process described in the U.S. Pat. No. 5,702,667 relies on the treatment of the outer peripheral surface and the inner circumferential surface to produce hardened areas at the ends of the bushing. However, the reliance on the treatment of the outer peripheral surface and the inner circumferential surface makes it difficult to control the characteristics of the hardened areas created on the ends of the bushing. For example, the hardened areas created on the ends of the bushing tend to extend to far into the hardened areas created on the outer peripheral surface and the inner circumferential surface and thus create exposed softened areas in the outer peripheral surface and the inner circumferential surface. These created softened areas are subject to excessive wear which in turn increases the cost of maintaining the work machine.
What is needed therefore is a method for hardening a bushing which overcomes one or more the above-mentioned drawbacks.
In accordance with one embodiment of the present invention, there is provided a method of hardening a work piece having (i) an outer surface, (ii) an inner surface which defines a passageway extending through the work piece, and (iii) an end. The method includes the steps of (A) advancing the work piece through a first induction coil such that a first hardened area is formed on the work piece, (B) advancing a second induction coil into the passageway of the work piece such that a second hardened area is formed on the work piece, and (C) positioning a third induction coil adjacent to the end of the work piece such that a third hardened area is formed on the work piece. The positioning the third induction coil step is performed after (i) the advancing the work piece through the first induction coil step and (ii) the advancing a second induction coil into the passageway step.
In accordance with another embodiment of the present invention, there is provided a track chain. The track chain includes a bushing having (i) an outer surface, (ii) an inner surface which defines a passageway extending through the bushing, and (iii) an end. The bushing is prepared by a process including the steps of (i) advancing the bushing through a first induction coil such that a first hardened area is formed on the bushing, (ii) advancing a second induction coil into the passageway of the bushing such that a second hardened area is formed on the bushing, and (iii) positioning a third induction coil adjacent to the end of the bushing such that a third hardened area is formed on the bushing. The positioning the third induction coil step is performed after (i) the advancing the bushing through the first induction coil step and (ii) the advancing a second induction coil into the passageway step.
In accordance with yet another embodiment of the present invention, there is provided a work machine. The work machine has a track chain which includes a bushing having (i) an outer surface, (ii) an inner surface which defines a passageway extending through the bushing, and (iii) an end. The bushing is prepared by a process including the steps of (i) advancing the bushing through a first induction coil such that a first hardened area is formed on the bushing, (ii) advancing a second induction coil into the passageway of the bushing such that a second hardened area is formed on the bushing, and (iii) positioning a third induction coil adjacent to the end of the bushing such that a third hardened area is formed on the bushing. The positioning the third induction coil step is performed after (i) the advancing the bushing through the first induction coil step and (ii) the advancing a second induction coil into the passageway step. The work machine also includes a sprocket positioned in contact with the track chain.